The present invention relates to a casting method in high-pressure casting such as die casting or squeeze casting.
In high-pressure casting such as die casting or squeeze casting, if a molten metal cast in a cavity is rapidly cooled and solidified, the molten metal does not reach edge portions of the cavity and the quality of the cast product is degraded. In order to prevent this, the molten metal is cast in the molds at high speed, and the molds and the casting sleeve are kept at a predetermined temperature. After casting, the molten metal must be rapidly cooled and solidified.
For this purpose, a heat-insulating material, a solid asbestos, or solid paper is adhered to molten metal contact surfaces of the conventional molds and sleeve, a mold release agent is applied thereto, the molds and sleeve are made of a ceramic material, or the molds and sleeve are heated by a heater.
Of these conventional heating techniques, when a ceramic material is used, a heat-retention effect can be obtained to some extent since the material has a small heat conductivity. However, such a material cannot provide a good cooling effect. When a heater is used, a good heat-retention effect can be obtained when the molds are heated to a temperature near that of the molten metal. In this case, rapid cooling at a high pressure cannot be properly performed. In addition, even if a heat-insulating material is adhered to the molten metal contact surfaces, rapid cooling cannot be expected. When the mold release agent is applied to the molten metal contact surfaces, burning of these surfaces can be prevented. However, heat retention and rapid cooling cannot be properly performed. When asbestos is adhered to the molten metal contact surfaces, a good heat-retention effect can be obtained. However, when a temperature exceeds 500.degree. C., asbestos is oxidized to generate a gas. The gas or the burnt asbestos is mixed in the molten metal to cause product defects. In addition, the burned and carbonized pieces are attached to the molds to decrease heat conductivity, thereby preventing rapid cooling. When paper is adhered to the molten metal contact surfaces, paper is subjected to oxidation and decomposition at a high temperature and a toxic gas is generated.